Think CS in C#

Think CS in C##

Welcome to Think Computer Science in C#.

This book, originally inspired by the work of Andrew N. Harrington and George Thiruvathukal [1], serves as an introductory computer programming textbook at college level.

Designed for students who are formally introduced to programming and computer science for the first time, this book focuses on covering the fundamental concepts of computer science and programming with clarity, structure, and relevance, to help students achieve good understanding of core computing and programming principles.

Although modern AI platforms are becoming strong in automated code generation, system engineers, data scientists, and cybersecurity experts with great problem-solving skills will always be needed; and it all begins with the fundamental knowledge of computing and the capability to code.

C#

Albeit the overall popularity of JavaScript and Python, Java and Microsoft .NET remain as strong technologies for large enterprises. In recent years, especially, Microsoft has made C# the central language for their fast-evolving, open-sourced, and cross-platform .NET ecosystem.

C# is a general-purpose, high-level, multiple-paradigm, and is gaining market share as a popular programming language. C# has been used in creating interactive websites, mobile apps, video games, augmented reality (AR) & virtual reality (VR), desktop applications, and back-end services. Specifically, C# is widely used in building cross-platform applications, web services, and game development. For example, the mobile game Pokémon Go is built with the Unity game engine and the Stack Overflow website is built with ASP.NET, and both frameworks use C# as their programming language.

In the annual Stack Overview Developer Survey[2], for example, C# stays as strong general-purpose languages.

Hide code cell source

 
using System.Net.Http;
using System.Text.RegularExpressions;
using Plotly.NET;
using Plotly.NET.Interactive;
using Plotly.NET.LayoutObjects;

var surveyUrl = "https://survey.stackoverflow.co/2025";
var topLangs = new List<(string Language, double Percent)>();

var targetLanguages = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
{
    "JavaScript", "HTML/CSS", "SQL", "Python", "Bash/Shell",
    "TypeScript", "Java", "C#", "C++", "PowerShell"
};

try
{
    using var http = new HttpClient();
    http.DefaultRequestHeaders.UserAgent.ParseAdd("Mozilla/5.0 (compatible; CSCSBook/1.0)");
    var html = await http.GetStringAsync(surveyUrl);

    // Parse language entries such as "JavaScript 66%" that appear in chart payload/content.
    var matches = Regex.Matches(
        html,
        @"(JavaScript|HTML/CSS|SQL|Python|Bash/Shell(?:\s*\(all shells\))?|TypeScript|Java|C#|C\+\+|PowerShell)\s*([0-9]+(?:\.[0-9]+)?)%",
        RegexOptions.IgnoreCase
    );

    foreach (Match m in matches)
    {
        var rawLanguage = m.Groups[1].Value.Trim();
        var language = rawLanguage.StartsWith("Bash/Shell", StringComparison.OrdinalIgnoreCase) ? "Bash/Shell" : rawLanguage;
        if (!targetLanguages.Contains(language)) continue;

        var pct = double.Parse(m.Groups[2].Value);
        if (!topLangs.Any(x => x.Language.Equals(language, StringComparison.OrdinalIgnoreCase)))
            topLangs.Add((language, pct));
    }
}
catch
{
    // Network or parsing failures should not break the notebook build.
}

if (topLangs.Count < 10)
{
    // Fallback top-10 values (Stack Overflow Developer Survey 2025, published summary/chart).
    topLangs = new List<(string, double)>
    {
        ("JavaScript", 66.0),
        ("HTML/CSS", 61.9),
        ("SQL", 58.6),
        ("Python", 57.9),
        ("Bash/Shell", 48.7),
        ("TypeScript", 43.8),
        ("Java", 29.5),
        ("C#", 27.9),
        ("C++", 23.6),
        ("PowerShell", 23.3),
    };
}

var ordered = topLangs
    .OrderByDescending(x => x.Percent)
    .Take(10)
    .OrderBy(x => x.Percent)
    .ToArray();

var langs = ordered.Select(x => x.Language).ToArray();
var pcts = ordered.Select(x => x.Percent).ToArray();

Chart2D.Chart.Bar<double, string, string, string, string>(
    values: pcts,
    Keys: langs,
    Name: "% Used"
 )
.WithLayout(Layout.init<string>(
    Width: 500, Height: 320,
    Title: Title.init("Top 10 Languages - Stack Overflow Survey 2025", X: 0.5, Y: 0.95),
    Margin: Margin.init<int, int, int, int, int, int>(Top: 60, Right: 30, Bottom: 50, Left: 140)
)).WithXAxis(LinearAxis.init<string, string, string, string, string, string, string, string>(
    Title: Title.init("% of Respondents")
))
.WithYAxis(LinearAxis.init<string, string, string, string, string, string, string, string>(
))
.WithConfig(Config.init(Responsive: false))
.Display();

Also, according to TIOBE Index, C# is one of the most popular languages according to the number of search engine hits.

Hide code cell source

 
using System.Reflection;
using System.Runtime.CompilerServices;
using HtmlAgilityPack;
using Plotly.NET;
using Plotly.NET.Interactive;
using Plotly.NET.LayoutObjects;

var web = new HtmlWeb();
var doc = web.Load("https://www.tiobe.com/tiobe-index/");

var rows = doc.DocumentNode.SelectNodes("//table[contains(@class,'table-top20')]//tr");

var languages = new List<string>();
var ratings = new List<double>();

foreach (var row in rows.Skip(1))
{
    var cells = row.SelectNodes("td");
    if (cells != null && cells.Count >= 6)
    {
        languages.Add(cells[4].InnerText.Trim());
        if (double.TryParse(cells[5].InnerText.Replace("%", "").Trim(), out double rating))
            ratings.Add(rating);
    }
}

var top10Languages = languages.Take(10).Reverse().ToArray();
var top10Ratings = ratings.Take(10).Reverse().ToArray();

var chart = Chart2D.Chart.Bar<double, string, string, string, string>(
    values: top10Ratings,
    Keys: top10Languages,
    Name: "TIOBE Index"
)
.WithTitle("TIOBE Programming Community Index")
.WithLayout(Layout.init<string>(
    Width: 500,
    Height: 320,
    Title: Title.init("TIOBE Programming Community Index", X: 0.5, Y: 0.95),
    Margin: Margin.init<int, int, int, int, int, int>(Top: 60, Right: 20, Bottom: 50, Left: 120)
)).WithXAxis(LinearAxis.init<string, string, string, string, string, string, string, string>(
    Title: Title.init("Rating (%)")
))
.WithYAxis(LinearAxis.init<string, string, string, string, string, string, string, string>(
))
.WithConfig(Config.init(Responsive: false));
// chart.Show();
chart.Display();

Footnotes